. Soil physics and management. Map showing the three centers of ice accumulation in North and Salisbury. Courtesy Henry Holt & Co.) (Cham- center and was the most extensive in the middle west during theentire period of glaciation. The greatest area of surface deposits isin Illinois, hence the name. It is exposed in Oliio, and Indiana, glaciation was followed by a long interglacial stage duringwhich weathering and soil formation occurred. It is known as 48 SOIL PHYSICS AND xMAXAGExMENT the Sangamon stage (Fig. 4-1:). Peat deposits have been found asmuch as ^v feet in t
. Soil physics and management. Map showing the three centers of ice accumulation in North and Salisbury. Courtesy Henry Holt & Co.) (Cham- center and was the most extensive in the middle west during theentire period of glaciation. The greatest area of surface deposits isin Illinois, hence the name. It is exposed in Oliio, and Indiana, glaciation was followed by a long interglacial stage duringwhich weathering and soil formation occurred. It is known as 48 SOIL PHYSICS AND xMAXAGExMENT the Sangamon stage (Fig. 4-1:). Peat deposits have been found asmuch as ^v feet in thickness that Avere formed during this period,(d) lowan Glaciation. Loess Deposits and Peorian Inter-glacial Stage.âThe Sangamon interghieial stage was followedby the lowan advance from the Keewatin center and covered a con-siderable part of Minnesota. Wisconsin, northeastern Iowa and thenorthern part of Illinois. The conditions at the time of the meltingof this glacier gave rise to extensive loess deposits. During sum-. Fio. 43.âMap showing extent of ice-sheet, Europe. (Reproduced from Danas Manual ofCJeolog}-, by special ammgement with American Book Company.) nier the melting was very rapid so that the Hood plains of streamsdraining from the glacier received deposits of rock Hour duringthese periods of overflow. During times of little melting thestreams contracted to their ordinary channels, leaving the materialexposed on their flood pdains. This was picked up by the wind anddistributed over the upland where it occurs as a deposit from 3 toloO feet in thickness over part of the states bordering the ^fississippiand Missouri Eivers. The loess buried the Sang-amon soil. The Peorian interglacial stage followed the lowan glaciation. GLACIAL OR ICE-LAID DEPOSITS 49
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